Motor Function Assessment in Patients with Congenital Myopathy: Application of Clinical Scales, Dynamometry, and Bioimpedance

Abstract

Introduction

Congenital myopathies are a heterogeneous group of hereditary neuromuscular disorders, diagnosed based on clinical, histopathological, and genetic findings. They are classified according to histopathological alterations such as the presence of cores or minicores (core myopathy), centralized nuclei (centronuclear myopathy or central core disease), nemaline rods or bodies (nemaline myopathy), as well as variants with inclusions or nonspecific changes. These entities may share mutations in different genes.
Their phenotypic expression is broad. Clinically, they often present with neonatal hypotonia, early-onset axial and proximal muscle weakness, and delayed motor development. These manifestations may appear from birth, childhood, or adolescence, and in some cases during adulthood, with forms ranging from mild to severe.

Objective

To evaluate the motor capacity of patients with congenital myopathy treated at the National Institute of Rehabilitation (INR), using the Motor Function Measure (MFM) and the NorthStar Ambulatory Assessment (NSAA). Additionally, in patients over 12 years old, muscle strength was assessed by dynamometry and body composition was analyzed by bioimpedance.

Methodology

An observational, cross-sectional, and descriptive study was conducted in patients with a confirmed diagnosis of congenital myopathy through clinical evaluation, muscle biopsy, and/or genetic testing. Two functional scales were applied: the MFM scale with 20 items for children under 6 years and 32 items for individuals aged 6 to 60 years, both evaluating three domains (D1: standing and transfers, D2: axial and proximal motor function, D3: distal motor function), and the NSAA scale, applied only to ambulatory patients.

In patients older than 12 years, manual dynamometry was used to evaluate bilateral muscles (biceps, deltoid, pectoralis, gluteus medius, quadriceps, and tibialis anterior), and bioimpedance analysis was performed to estimate body composition, including muscle mass, fat mass, and total body water percentage.

Results

Among the 12 patients (4 females and 8 males) aged 3 to 41 years, the average scores in the MFM-20 were: D1 33.3%, D2 77.08%, D3 66.6%, with a total score of 57.5%. For the MFM-32, the average scores were 41.53% in D1, 77.27% in D2, 82.85% in D3, and a total of 65.82%. The average score on the NSAA scale was 15 out of 34 points. Bioimpedance analysis revealed a significant reduction in muscle mass and body hydration among the evaluated patients. Strength measurements using dynamometry showed decreased muscle strength in the assessed muscle groups.

Conclusions

Functional assessment using the MFM and NSAA scales allowed for objective quantification of motor capacity in patients with congenital myopathy, revealing moderate to severe disability. In patients over 12 years of age, dynamometry confirmed muscle weakness, providing complementary data for more accurate follow-up. Bioimpedance revealed a significant reduction in muscle mass and hydration, reflecting the systemic impact of the disease. These findings highlight the importance of a multidimensional evaluation combining clinical scales and functional tests, contributing to comprehensive management, ongoing functional monitoring of patients, and in the future, the evaluation of new treatment efficacy.